#include<stdio.h>
int main()

{
	double  a, b, c, p;
	scanf("%lf", &a );
	scanf("%lf", &b);
	scanf("%lf", &c);
	p = (a+b+c) / 2;
	printf("%.2lf", p*(p - a)*(p - b)*(p - c));

    return 0;


}